Bei einem anderen E90 wohl bei der Sirene am Hinterrad:
Final word on the tilt sensor
If you have the factory alarm - you have a tilt sensor.
It is located in the module with the siren, which is located at the top of the DS wheel well, beneath the wheel well liner. If you remove that rear liner you will see the siren/module bolted to the wheel well @ 12 o'clock TDC above wheel.
Zum E87 kann ich nichts besonders finden - nehme an das der da auch sitzt.